Method and apparatus for concentrating fibrous suspensions



March 1, 1966 N. A. 1.. WIKDAHL 3,237,753

METHOD AND APPARATUS FOR CONCENTRATING FIBROUS SUSPENSIONS Filed July 6, 1962 2 Sheets-Sheet 2 Fig.2

lawn/r01? Mu IQA/D-"RS LEA/Amer M/wma United States Patent 0 F 3,237,763 METHOD AND APPARATUS FOR CONCEN- TRATING FIBRGUS SUSPENSIONS Nils Anders Lennart Wikdahl, Bravallavagen 42, Djarsholrn, Sweden Filed July 6, 1962, Ser. No. 207,973 14 Claims. (Cl. 299-12) The present invention relates to a method of treating suspensions such as paper pulp and similar suspensions and to an installation for carrying out the method. More particularly, the invention relates to a method of cleaning or purifying and concentrating fibrous suspensions by first removing the impurities from the suspension in a cleaning aggregate including hydrocyclone separating means and screening means coupled to the inlet side of the separating means, and then concentrating or thickening the suspension by extracting liquid therefrom in concentrating or extracting means. The invention further relates to an installation for carrying out the particular method of the invention.

According to the invention, the suspension to be treated is first supplied to a receiving vat in which it is diluted with water supplied from a regulating container in which the water level is held to a predetermined maximum level by means of an overflow within the regulating container. The diluted suspension is fed in succession to and through the cleaning aggregate by means of a pump interposed between the vat and the cleaning aggregate and then to a concentrating means in which water is extracted. As is apparent, the cleaning aggregate, the pump and the concentrating means constitute a flow system closed to the atmosphere in which the inlet of the cleaning aggregate is connected to the pump and the outlet to the concentrating means. Due to the dilution of the fibrous suspension in the receiving vat, the volume of suspension discharged from the vat is greater than the volume of suspension supplied to the vat. Accordingly, the capacity of the pump must be greater than the volume of suspension per time-unit supplied to the vat. Consequently, a how of water from the regulating container to the vat is caused and at the same time the escape of fibrous suspension into the overflow of the regulating container is prevented. By supplying a substantially constant volume of fibrous suspension of substantially uniform concentration to the receiving vat and suitably selecting the cross section of the communication between the vat and the regulating container, a practically constant relative proportion between the fibrous suspension and the diluting water is maintained independent of possible fluctuations in the volume of water supplied to the regulating container from the concentrating means, provided only that this feed of water is not so small that there is no discharge of water through the overflow. This affords the advantage that without using any regulating means other than the overflow, the concentration of the fibrous suspension supplied to the cleaning aggregate through the pumping means is maintained at the desired level.

It is further possible and convenient to use as diluting water, the water that is extracted in the concentrating device by discharging this extracted water directly into the regulating container. In order to make up for losses unavoidable in practice, the concentration of fibrous sus- 3,237,753 Patented Mar. 1, 1966 pension discharged from the concentrating means should be at least somewhat higher than the concentration of the fibrous suspension supplied to the vat for processing. However, such increase in concentration at the discharge of the concentrating means is not necessary if diluting water is supplied to the vat from some external source.

The method of the invention affords the advantage of a considerable simplification of the installation in which the method is carried out since the heretofore customary rather complicated regulating means may be eliminated. The method of the invention also produces considerably better cleaning results since the concentration of the suspension that is supplied to the cleaning aggregate fluctuates much less than in methods heretofore used.

According to the invention, the cyclone separating means in the cleaning aggregate are preferably disposed at a level higher than the overflow in the regulating container. When the separation is effected in two or more successive stages, the reject flow from a preceding stage is fed to the next stage by means of separate pump means. According to the invention, the reject outlets in each preceding stage are connected to the regulating container, thereby maintaining the fluctuations of the liquid level and of the pressure in reject outlets at a minimum and also causing a substantially constant or fixed liquid level in the inlet of the pump means of a succeeding stage.

In order to carry out the method of the invention and to obtain the aforementioned advantages, an installation of the invention is so arranged that the suspension is supplied to and forced through the cleaning aggregate by means of a pump connected with its suction side to the receiving vat and with its pressure side to the inlet side of the cleaning aggregate, the output side of which is connected to the concentrating device, thereby forming the aforedescribed closed flow system.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and set forth in the appended claims constituting part of the application.

In the accompanying drawing several preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a how sheet of an installation according to the invention;

FIG. 2 is a diagrammatic elevational side view of an installation according to the invention; and

FIG. 3 is a plan view of FIG. 2 shown in a somewhat simplified manner.

Referring first to FIG. 1, the flow sheet according to this figure shows a vessel 1 which is divided by a partition wall 2 in a receiving vat 4 and a regulating container further sub-divided by a partition wall 3 in compartments 5 and 6. Partition wall 2 terminates short of the bp ttom of vessel 1 so that vat 4 and containers 5, 6 constitute communicating compartments. Partition wall 3 terminates short of the upper edge of the side walls of vat 1 whereby partition wall 3 constitutes in effect an overflow for the liquid in the communicating vat 4 and compartment 5, or in other words, the height of partition wall 3 controls the maximum liquid level in vat 4 and compartment 5. Liquid is discharged from compartment 6 through an outlet 11.

Instead of partition wall 3 and outlet 11, an overflow pipe could also be provided in the open container formed by compartments 5 and 6. Conduits 8, 9 and 10 connect receiving vat 4 with the inlet or suction side of three pumps 12, 13 and 14, the outlet or pressure side of which is connected by conduits 15, 16 and 17 to screening devices 18, 19 and 20 respectively. The output of the screening devices is fed by means of conduits 21, 22, 23 to the inlet side hydrocyclone separating means 24, 25 and 26 respectively. Each of the separating means is shown as including three separators coupled in parallel, but a greater or smaller number of separators may be provided in each separating means. The cleaned or purified component of the suspension, the so-called overflow or accept is fed through conduits 27, 28 and 29 respectively directly to a thickening or concentrating means 30 in which water is extracted from the suspension. The resulting concentrate is discharged from the concentrating device through an outlet 31 and the extracted water is discharged from the concentrating device into the regulating containers 5, 6 through an outlet '32.

The so-called underflow or reject is fed from the separating means 24, 25 and 26 through conduits 33 and 34 and a pump 35 to a second hydrocyclone separating means 36 shown as comprising two separators. The accept from the separating means 36 is returned to receiving vat 4 through a conduit 37 and the reject from the separating means 36 is fed through conduits 38, 39 and a pump 40 to a third hydrocyclone separating means 41 shown as comprising one separator for still further separation. The accept from the third separating means is fed to the inlet side of pump 35 through a conduit 42 and the reject of the separating means is discharged through a conduit 80.

Water taken from open containers 5, 6 may be added through conduit 43 to the flow in conduits 33 and 38.

Flushing water may be supplied to the underflow or reject outlets of the separators of the second and third separating means 36 and 41 through a conduit 44.

All the hydrocyclone separators may be equipped. with means for periodically repeated cleaning of the underflow or reject outlets thereof. Means for such periodic cleaning are indicated by cut-off valves 45, 46, 47, 48 and 49 which are shown included in the outlet for the overfiow or accept component. The valves may be operated by pressure air and may be cycled by a pulse-distributing apparatus 50 operatively connected with the same. Suitable oleaning devices of this kind are more fully described in co-pending application Serial No. 590,650, filed June 11, 1956 by the applicant herein.

The outlets for the material discharged from screening devices 18, 19 and 20 and containing coarser impurities are connected by conduits 51, 52 and 53 directly to separate hydrocyclone separators 54, 55 and 56, respectively, which may also be provided with conventional means for supplying flushing water. The cleaned output of separators 54, 55 and 56 is returned. through conduits 57, 58 and 59 to the inlet or suction side of pumps 12, 13 and 14.

The screening devices 18, 19 and 241 are preferably pressure-operated screening devices. Devices of this kind are well known. They may comprise a perforated drum which is stationarily mounted in a housing and on the inside of which rotary agitators are disposed to prevent clogging of the perforated drum. The construction of the pressure-operated screening devices as such does not constitute part of the invention. The use of pressure-operated screening devices affords the advantage that the hydrocyclone separators can be connected directly to the outlets of the screening devices, provided that pumps 12, 13 and 14 are laid out in accordance with the total drop of pressure through the screening devices and the hydrocyclone separators connected thereto.

As is indicated in FIG. 1, suitably arranged valves and throttling members should be included in the flow system.

The installation as described in connection with FIG. 1 operates as follows:

Assuming that, for instance, a fibrous suspension such as a paper pulp suspension received from the bleaching plant of a paper pulp factory is to be treated, the suspension is supplied. through conduit 7 to receiving vat 4 in which it is diluted by water fed from the concentrator 30 through outlet 32 into regulating containers 5, 6 from which it passes into vat 4 by means of the passageway defined by partition wall 2, The diluted suspension is forced by the pumps through screening devices 18, 19 and 20 and the screened-out coarser impurities are fed directly to further hydrocyclone separators 54, 55 and 56 through conduits 51, 52 and 53. The fiber content separated in separators 54, 55 and 56 is returned to the inlet or suction side of pumps 12, 13 and 14.

As has been previously pointed out, the overflow wall 3 in regulating containers 5, 6 limits the liquid level in container 5 to a maximum level and hence also in vat 4 communicating with the container. The liquid level in container 5 is maintained at the maximum level due to a continuous flow of liquid. through outlet 32 into container 5 and from this container across the top of overflow wall 3 to container 6 and outlet 11. Accordingly, the liquid level in container 5 remains substantially constant. As a result, the concentration of the suspension supplied to pumps 12, 13 and 14 is also maintained substantially constant. Hence, pumps 12, 13 and 14 and, thus, the entire cleaning aggregate will operate at practically constant conditions. Such constancy of the operating conditions is further improved by connecting the underflow or reject outlets of the hydrocyclone separators in the first and the second stage through a conduit 43 to the regulating containers 5, 6 and thereby also with vat 4, thus maintaining a substantially constant level in the underflow or reject outlets also. As a result of such stabilized operating conditions of the hydrocyclone separators, the cleaning action is markedly improved.

Turning now to FIGS. 2 and 3, these figures show diagrammatically an actual installation according to the invention. Vessel 60 of FIGS. 2 and 3 corresponds to vessel 1 of FIG. 1. Accordingly, the vessel is divided by partition walls similar to the partition Walls of FIG. 1 in a receiving vat 66a and a regulating container 60b and 60c including the overflow. The fibrous suspension is fed to container 60a through a pipe 61. Pipe 62 indi cates one of the pipes which feed the fibrous suspension diluted with Water from vat 60a to a pressure screen 65 by means of a pump 63 and a pipe 64 connected to the outlet or pressure side of the pump. The pressure screen may be again of the perforated drum type previously described. The fibrous suspension is supplied to the inside of the perforated drum where the separated coarser impurities are collected and from which they are discharged through a separate outlet pipe 78 and fed to a hydrocyclone separator 66. The accept or overflow of this separator is returned. to pipe 62 by means of a pipe 67. The output of pressure screen 65 from which primarily the coarser impurities have been removed is fed to a hydrocyclone separator aggregate 69 through a pipe 68. The separator aggregate 69 is preferably of the type described in Reissue Patent 25,099, that is, it comprises a great number of comparatively small hydrocyclone separators which are coupled in parallel with each other. The overflow or accept output of aggregate 69 is fed through a conduit 70 to a thickener or concentrator 71 which is disposed directly above vessel 60 so that the water extracted in the concentrator can be discharged into regulating container 60b by gravity feed. The underflow or reject output of aggregate 69 is forced by means of a pump 73 into a further cyclone separator aggregate 74 which constitutes a second separation stage. Aggregate 74 may be of generally the same design as aggregate 69 but preferably includes a smaller number of hydrocyclone separators.

The overflow or accept output of the second separation stage is returned to receiving vat 60a through a conduit 75 and the underiiow or reject output is fed to a third separation stage by means of a pump 76. In the installation according to FIGS. 2 and 3 the cyclone separators in the third stage are also arranged in the aggregate 74, but there are preferably fewer separators in the third stage than in the second stage.

As is shown in FIG. 3, two aggregates 74 are provided and both aggregates include half the separators of the second and third stage, respectively. This affords the advantage that the aggregates are exactly alike in both stages and that if desirable or necessary, one of the aggregates can be disconnected. without completely stopping the operation.

It may be necessary or at least advantageous to have at least two cyclone separator aggregates in the first stage also. There are shown in FIG. 3 three aggregates 69 in the first stage, each equipped with its own pump 63 in its own pressure screen 65. This permits a layout of the installation such that the same can be kept operating at least temporarily if one of the aggregates must be set still. This arrangement is particularly advantageous when cleaning or unclogging of the underflow or reject outlets of the separators is effected by intermittently throttling the overflow outlets by means of the distributor 50 shown in FIG. 1. With this type of cleaning, throttling results in a greater pressure increase and, hence, in a more effective flushing when each aggregate has its own pump.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention, it will :be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of treating a fibrous suspension, said method comprising the steps of providing a receiving vat, pumping means, screening means and hydrocyclone separating means connected in a how system closed to the atmosphere, the pumping means being directly connected to the receiving vat, feeding the suspension to be treated first to the receiving vat, then pumping the suspension from said receiving vat by the pumping means first through the screening means for screening out coarse impurities in the suspension and then the screened suspension through the hydrocyclone separating means, said separating means delivering an accept flow and a reject flow, then feeding the accept flow to concentrating means for extracting liquid from the suspension, and then discharging the concentrate from the concentrating means, and also comprising the steps of feeding liquid to a flow regulating container communicating with the receiving vat to dilute the suspension therein and including an overflow means limiting the liquid level in the regulating container and thus in the receiving vat communicating therewith to a predetermined maximum level and also maintaining the concentration of the suspension in the receiving vat substantially constant.

2. The method according to claim 1 in which the separation of the fibrous suspension in the hydrocyclone separating means is effected in several successive stages, and further comprising the step of connecting the reject flow from at least one stage preceding the last stage to said regulating container for controlling the rate of feed flow by the liquid level in said container as controlled by the overfiow means therein.

3. The method according to claim 1 and also comprising the step of discharging liquid extracted in the 6 concentrating means into the receiving container to dilute the suspension fed to the receiving vat.

4. The method according to claim 1 and comprising the step of pressure feeding coarse impurities screened out in said screening means to further hydrocyclone separating means for recovering fibrous material entrained in said coarse impurities, and then returning said recovered fibrous material to the closed flow system.

5. The method according to claim 4 and comprising the further step of continually adding flushing water to the reject outlet of said further hydrocyclone separating means to increase the recovery of fibrous material.

6. An installation for treating a fibrous suspension, said installation com-prising a receiving vat for feeding thereto a flow of fibrous suspension to be treated, a pump means directly connected to the vat, a screening and separating aggregate including screening means for screening out coarse impurities in the suspension and hydrocyclone separating means for separating suspension fed thereto into accepts and rejects, said screening means having an inlet and an outlet and said hydrocyclone separating means having an inlet, an accept outlet and a reject outlet, the outlet of the screening means being connected to the inlet of the separating means for feeding the screened suspension to the separating means, concentrating means for extracting liquid from the accept suspension including an outlet for discharging concentrated suspension therefrom, conduit means connecting in sequence the receiving vat through the pump means to the inlet of the screening means of said aggregate, and the accept outlet of the separating means in said aggregate to said concentrating means in a flow system closed to the atmosphere; a regulating container communicating with said receiving vat; conduit means for feeding liquid to said container; and an overflow means in said container to control the maximum liquid level in said container and in the vat communicating therewith.

7. An installation according to claim 6 wherein said vat is disposed at a higher level than said pumping means to increase the rate of the liquid flow through the conduit means by gravity feed.

8. An installation according to claim 6 wherein conduit means connect the reject outlet of the separating means to said regulating container.

9. An installation according to claim 6 wherein said concentrating means has an outlet communicating with said container for discharging liquid extracted in the concentrating means into the container, said concentrating means being disposed above the container to effect a discharge fiow by gravity feed.

10. An installation according to claim 6 wherein the overflow means of said container is in the form of a partition wall within the container terminating short of the upper end thereof, said communication between the container and the vat being formed by a common partition Wall between the container and the vat terminating short of the bottom wall of the container.

11. An installation according to claim 6 wherein said screening means comprise screens operated at elevated pressure, said screening means having an outlet for impurities liberated from the fibrous suspension and an outlet for the purified suspension, both the impurities and the purified suspension being discharged from the screening means at a pressure above atmospheric pressure, and wherein a further separating means having a reject outlet is connected to said outlet for impurities for separating fibers contained in the impurities in said further separating means.

12. An installation according to claim 11 and comprising flushing means for continually supplying flushing water to the reject outlet of said further separating means.

13. An installation according to claim 6, wherein said hydrocyclone separating means are arranged in at least two stages, the separating means in one of said stages including several separators arranged in at least two groups, said pump means including at least two pumps and said screening means at least two screens, and wherein conduit means connect said groups of separators, said pumps and said screens in at least two parallel flowing systems each including a pump, a screen and a separator.

14. An installation according to claim 6, wherein said separating means and said concentrating means are disposed at the same level, and wherein said conduit means connecting said receiving vat and said pump are disposed at a lower level.

References Cited by the Examiner UNITED STATES PATENTS Miller 209-163 Clark 209211 Martindale 210-415 Marot 209-172.5

Wo odruff 209211 FRANK W. LUTTER, Primary Examiner.

HARRY B. THORNTON, Examiner. 

6. AN INSTALLATION FOR TREATING A FIBROUS SUSPENSION, SAID INSTALLATION COMPRISING A RECEIVING VAT FOR FEEDING THERETO A FLOW OF FIBROUS SUSPENSION TO BE TREATED, A PUMP MEANS DIRECTLY CONNECTED TO THE VAT, A SCREENING AND SEPARATING AGGREGATE INCLUDING SCREENING MEANS FOR SCREENING OUT COARSE IMPURITIES IN THE SUSPENSION AND HYDROCYCLONE SEPARATING MEANS FOR SEPARTING SUSPENSION FED THERETO INTO ACCEPTS AND REJECTS, SAID SCREENING MEANS HAVING AN INLET AND AN OUTLET AND SAID HYDROCYCLONE SEPARTING MEANS HAVING AN INLET, AN ACCEPT OUTLET AND A REJECT OUTLET, THE OUTLET OF THE SCREENING MEANS BEING CONNECTED TO THE INLET OF THE SEPARATING MEANS FOR FEEDING THE SCREENED SUSPENSION TO THE SEPARATING MEANS, CONCENTRATING MEANS FOR EXTRACTING LIQUID FROM THE ACCEPT SUSPENSION INCLUDING AN OUTLET FOR DISCHARGING CONCENTRATED SUSPENSION THEREFROM, CONDUIT MEANS CONNECTING IN SEQUENCE THE RECEIVING VAT THROUGH THE PUMP MEANS TO THE INLET OF THE SCREENING MEANS OF SAID AGGREGATE, AND THE ACCEPT OUTLET OF THE SEPARATING MEANS IN SAID AGGREGATE TO SAID CONCENTRATING MEANS IN A FLOW SYSTEM CLOSED TO THE ATMOSPHERE; A REGULATING CONTAINER COMMUNICATING WITH SAID RECEIVING VAT; CONDUIT MEANS FOR FEEDING LIQUID TO SAID CONTAINER; AND AN OVERFLOW MEANS IN SAID CONTAINER TO CONTROL THE MAXIMUM LIQUID LEVEL IN SAID CONTAINER AND IN THE VAT COMMUNICATING THEREWITH. 